1. Field of the Invention
This invention is generally directed to optical fiber sensors, and more specifically relates to an optical fiber sensor having a light conducting core and a coating of cladding material, with a length of a sensing material applied to the distal portion of the optical fiber core.
2. Description of Related Art
Measurement of concentrations of an analyte in a fluid mixture has become an important part of modern medicine. For example, it has been found that the concentration of oxygen in the blood can be measured from the property of certain dye indicators to fluoresce at particular wavelengths of light when irradiated by light of a specific wavelength range, and from the property of oxygen to quench this fluorescence. Intravascular catheters incorporating such dye indicators and optical fibers have been devised for monitoring blood oxygen levels, blood CO.sub.2 levels and parameters such as pH.
Optical fibers are generally formed with an inner light conducting core and an outer light refracting or light reflecting cladding material. One previous approach to construction of an optical fiber sensor involves the attachment of a dye filled porous glass to the tip of the optical fiber, such as by an adhesive. However, this method allows the possibility of misalignment of the porous glass on the optical fiber, and the possibility of all or a portion of the porous glass becoming separated from the optical fiber due to mechanical perturbation. Another approach has involved the application of sensing material directly to the tip of the optical fiber, thereby adding to the radial dimension of the optical fiber tip. However, where such an optical fiber sensor is to be used for intravascular monitoring of blood oxygen levels, for example, it would be desirable for the sensor portion not to be larger than the optical fiber itself. Another approach has involved the attachment of a sleeve which contains the dye indicator sensing material in a matrix to the end of an optical fiber, such as by adhesive. However, this construction may also be dislodged due to mechanical perturbations, and entails a labor intensive manufacturing process.
From the above, it may be seen that the current methods of constructing optical fiber sensors which include sensor material distributed along the distal portion of the fiber are either labor intensive, fragile, present difficult quality control issues or some combination of these problems. Thus, there remains a need for an optical fiber sensor which may be more simply manufactured, such as by a dipping process, and which can provide good adhesion between the surface of the optical fiber core and the sensing material applied over it. It would also be desirable if the construction allowed control of the thickness of the sensor, and allowed formation of the sensor so as to conform to the shape and thickness of the optical fiber, to minimize mechanical perturbations, and to facilitate use of the sensor for intravascular monitoring of vital signs and parameters, such as blood oxygen levels.